In the making of aluminum in an electric reduction cell, it is normal to employ a crustbreaker or plugger foot which serves the purpose of breaking through a solidified crust on top of the molten bath. After a hole has been punched through the crust, additional alumina can be added to the bath so as to mix with the molten cryolite to form aluminum. The use of a crustbreaker or a plugger foot is known in the art as taught by U.S. Pat. No. 4,049,529 and British Pat. No. 1,262,069. It is also common to attach the plugger foot directly to the mechanical ore feeder as is shown in U.S. Pat. No. 3,681,229, Canadian Pat. No. 800,598 and Canadian Pat. No. 1,022,497. The typical plugger foot is a solid cast iron or steel projectile attached to the end of a vertically mounted steel rod. This design is very simple in construction, inexpensive and easy to manufacture. However, the drawback of the present plugger foot occurs when the cell or pot goes into an "anode effect". An anode effect occurs when the alumina ore within the molten bath decreases in percentage compared to the molten cryolite. This occurs as the electrolysis process takes place and the alumina is chemically used up. With less alumina in the bath, the voltage spikes from about 5 volts per cell to about 30 volts per cell. The easiest way to bring the voltage back to the normal level is to add more alumina to the bath. However, as the plugger foot punches a hole through the crust so that more alumina can be added, the higher voltage level transmitted from the bath through the metal plugger foot up into the feeder mechanism and causes arcing across various seals and pitting of various metal surfaces. This is detrimental to the feeder mechanism and air cylinder and necessitates replacement of the damaged components. Such replacement is both expensive and time-consuming.
Now a non-conductive plugger foot has been invented which prevents the transfer of electrical voltage from the molten bath to the feeder mechanism.